Actuation of a turbofan engine bifurcation to change an effective nozzle exit area

ABSTRACT

The invention relates to a turbine engine that includes a spool supporting at least one of a compressor and a turbine. A turbofan is coupled to the spool The spool is arranged in a core nacelle, and the turbofan is arranged upstream from the core nacelle. A fan nacelle surrounds the turbofan and the core nacelle and provides a bypass flow path. A structure extends radially between the core and fan nacelles to support the core nacelle relative to the fan nacelle. Surfaces are supported relative to the fixed structure and are moveable between closed and open positions to selectively obstruct bypass flow through the bypass flow path, thereby changing the effective area of the exit nozzle. A change in the effective area of the nozzle exit can be used to improve the efficiency and operation of the turbine engine.

This application claims priority to PCT Application Serial No.PCT/US2006/039802, filed on Oct. 12, 2006.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus and method for changing aneffective nozzle exit area of a turbofan engine.

A typical turbofan engine includes a core nacelle housing one or morespools supporting at least one compressor and turbine. One of the spoolsis used to rotationally drive a turbofan arranged upstream from the corenacelle. A fan nacelle surrounds the turbofan and the core nacelle. Thecore nacelle is supported by several bifurcations to centrally locatethe core nacelle relative to the fan nacelle. In addition to supportingthe core nacelle, the bifurcations are used to house various components,such as bleed air conduits and wires, for example. The bifurcations aretypically fixed, closed structures.

A generally annular bypass flow path is arranged between the core andfan nacelles through which bypass air from the turbofan flows. Thebifurcations are arranged in the bypass flow path. The bypass flow exitsfrom a nozzle exit area at the rear of the engine. The nozzle exit areais typically fixed in a turbofan engine.

Non-turbofan aircraft turbine engines have been developed that changethe effective nozzle exit area to affect the efficiency and operation ofthe engine. In military aircraft, for example, multiplecircumferentially arranged flaps at the exit of the engine nozzle arerotated inwardly and outwardly in a radial direction to change thephysical size of the nozzle's exit area. This arrangement addsadditional weight and cost to the engine externals. Many flaps arerequired as well as associated actuators. Further, the moveable flapsare external and subject to damage from foreign objects.

What is needed is a turbofan engine capable of changing the effectivenozzle exit area using existing engine structure and surfaces.

SUMMARY OF THE INVENTION

The invention relates to a turbine engine that includes a spoolsupporting at least one of a compressor and a turbine. A turbofan iscoupled to the spool. The spool is arranged in a core nacelle, and theturbofan is arranged upstream from the core nacelle. A fan nacellesurrounds the turbofan and the core nacelle and provides a bypass flowpath. In one example, a fixed structure or bifurcation extends radiallybetween the core and fan nacelles to support the core nacelle relativeto the fan nacelle.

In one example, opposing surfaces are supported relative to thebifurcation and are moveable between closed and open positions toselectively obstruct bypass flow through the bypass flow path, therebychanging the effective area of the nozzle. A change in the effectivearea of the nozzle can be used to improve the efficiency and operationof the turbine engine. In one example, the opposing surfaces aremanipulated in generally circumferential and axial directions about oneor more pivots in an arc in response to a controller commanding anactuator under predetermined conditions.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an example geared turbofan engine.

FIG. 2 is a front, cross-sectional view of the engine shown in FIG. 1.

FIG. 3A is one example flow control device taken along line 3-3 in FIG.1 and used to selectively change the effective nozzle exit area.

FIG. 3B is another example flow control device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A geared turbofan engine 10 is shown in FIG. 1. A pylon 38 secures theengine 10 to an aircraft. The engine 10 includes a core nacelle 12 thathouses a low spool 14 and high spool 24 rotatable about an axis A. Thelow spool 14 supports a low pressure compressor 16 and low pressureturbine 18. In the example, the low spool 14 drives a turbofan 20through a gear train 22. The high spool 24 supports a high pressurecompressor 26 and high pressure turbine 28. A combustor 30 is arrangedbetween the high pressure compressor 26 and high pressure turbine 28.Compressed air from compressors 16, 26 mixes with fuel from thecombustor 30 and is expanded in turbines 18, 28.

In the examples shown, the engine 10 is a high bypass turbofanarrangement. In one example, the bypass ratio is greater than 10:1, andthe turbofan diameter is substantially larger than the diameter of thelow pressure compressor 16. The low pressure turbine 18 has a pressureratio that is greater than 5:1, in one example. The gear train 22 is anepicycle gear train, for example, a star gear train, providing a gearreduction ratio of greater than 2.5:1. It should be understood, however,that the above parameters are only exemplary of a contemplated gearedturbofan engine. That is, the invention is applicable to other enginesincluding direct drive turbofans.

Airflow enters a fan nacelle 34, which surrounds the core nacelle 12 andturbofan 20. The turbofan 20 directs air into the core nacelle 12, whichis used to drive the turbines 18, 28, as is known in the art. Turbineexhaust E exits the core nacelle 12 once it has been expanded in theturbines 18, 28, in a passage provided between the core nacelle and atail cone 32.

The core nacelle 12 is supported within the fan nacelle 34 by structure36, which are commonly referred to as upper and lower bifurcations. Agenerally annular bypass flow path 39 is arranged between the core andfan nacelles 12, 34. The example illustrated in FIG. 1 depicts a highbypass flow arrangement in which approximately eighty percent of theairflow entering the fan nacelle 34 bypasses the core nacelle 12. Thebypass flow B within the bypass flow path 39 exits the fan nacelle 34through a nozzle exit area 40.

For the engine 10 shown in FIG. 1, a significant amount of thrust may beprovided by the bypass flow B due to the high bypass ratio. Thrust is afunction of density, velocity and area. One or more of these parameterscan be manipulated to vary the amount and direction of thrust providedby the bypass flow B. In one example, the engine 10 includes a structureassociated with the nozzle exit area 40 to change the physical area andgeometry to manipulate the thrust provided by the bypass flow B.However, it should be understood that the nozzle exit area may beeffectively altered by other than structural changes, for example, byaltering the boundary layer, which changes the flow velocity.Furthermore, it should be understood that any device used to effectivelychange the nozzle exit area is not limited to physical locations nearthe exit of the fan nacelle 34, but rather, includes altering the bypassflow B at any suitable location.

The engine 10 has a flow control device 41 (FIGS. 3A and 3B) that isused to effectively change the nozzle exit area. In one example, theflow control device 41 provides the fan nozzle exit area 40 fordischarging axially the bypass flow B pressurized by the upstreamturbofan 20 of the engine 10. A significant amount of thrust is providedby the bypass flow B due to the high bypass ratio. The turbofan 20 ofthe engine 10 is designed for a particular flight condition, typicallycruise at 0.8M and 35,000 feet. The turbofan 20 is designed at aparticular fixed stagger angle for an efficient cruise condition. Theflow control device 41 is operated to vary the nozzle exit area 40 toadjust fan bypass air flow such that the angle of attack or incidence onthe fan blade is maintained close to design incidence at other flightconditions, such as landing and takeoff. This enables desired engineoperation over a range of flight condition with respect to performanceand other operational parameters such as noise levels. In one example,the flow control device 41 defines a nominal converged position for thenozzle exit area 40 at cruise and climb conditions, and radially opensrelative thereto to define a diverged position for other flightconditions. The flow control device 41 provides an approximately 20%change in the exit nozzle area 40.

In the example shown in FIGS. 1 and 2, opposing bifurcations 52 radiallyextend between the core and fan nacelles 12, 34 to support the corenacelle 12 relative to the fan nacelle 34. Typically, bleed lines andother connections are housed within the bifurcations 52 to connect thecore nacelle 12 and its components with other areas of the aircraft. Thebifurcations 52 are arranged inside the fan nacelle 34 and are notexposed to potentially destructive foreign objects.

The flow control device 41 is used to change the effective nozzle exitarea, although the nozzle exit area 40 is fixed. In the examples shown,this is achieved by moving one or more surfaces supported, for example,by the bifurcation 52 to selectively obstruct portions of the bypassflow B through the bypass flow path 39. Any surface or surfaces exposedto the bypass flow path B can be used instead of or in addition to thebifurcation surfaces shown in FIGS. 3A and 3B.

In one example shown in FIG. 3A, opposing surfaces 56 connected to thebifurcations 52 by pivots 54 near a leading edge are moved by anactuator 58 between closed and open positions C, O. The pivot 54 isarranged on one end of opposing ends of each surface 56. A singleactuator is shown schematically connected to the surfaces 56 bylinkages. However, other configurations can be used. The surfaces 56move in an arc in generally axial and circumferential directions in theexamples shown. The actuator 58 is commanded by a controller 60 underpredetermined conditions to change the effective nozzle exit area withthe surfaces 56 to improve the efficiency and operation of the turbineengine 10.

In another example shown in FIG. 3B, the opposing surfaces 56 pivot neara trailing edge of the bifurcation 52. The arrangement shown in FIG. 3Bmay create a greater disturbance in the bypass flow B for the sameactuated distance as compared to the arrangement shown in FIG. 3A.

In this manner, the control device 41 uses surfaces of existing enginestructures in the turbine engine to minimize the additional weight andcost associated with providing a change in the effective nozzle exitarea.

Although example embodiments of this invention have been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

The invention claimed is:
 1. A turbine engine comprising: a spoolsupporting a turbine; a turbofan arranged upstream from the core nacelleand coupled to the spool; a fan nacelle surrounding the turbofan andproviding a bypass flow path between the fan and core nacelles having anozzle exit area; a flow control device including a surface in thebypass flow path movable between closed and open positions toeffectively change the nozzle exit area; and a bifurcation extendingbetween the core and fan nacelles to support the core nacelle relativeto the fan nacelle, the surface supported on the bifurcation, whereinthe bifurcation supports opposing surfaces on opposing sides of thebifurcation, each of the opposing surfaces having leading and trailingedges, each opposing surface movable about a pivot near the trailingedge between the closed and open positions in a generallycircumferential direction.
 2. The turbine engine according to claim 1,wherein the flow control device includes a controller programmed toinitiate movement of the surface between the closed and open positionsin response to a predetermined condition.
 3. The turbine engineaccording to claim 2, wherein the flow control device includes anactuator interconnected to the surface and communicating with thecontroller, the actuator adapted to receive a command from thecontroller in response to the predetermined condition.
 4. A method ofchanging the effective nozzle exit area of a turbine engine comprisingthe steps of: a) providing a bypass flow path circumventing a corenacelle; and b) moving opposing surfaces in the bypass flow path using asingle actuator operatively connected to the opposing surfaces toeffectively change a nozzle exit area associated with the bypass flowpath.
 5. The method according to claim 4, wherein step b) includesmoving the surface between open and closed positions in response to apredetermined condition.
 6. The method according to claim 4, comprisingthe step of supporting the surface on a bifurcation extending betweenthe core nacelle and the fan nacelle.
 7. The method according to claim4, wherein step b) includes moving the surface generallycircumferentially outward from the closed position to the open position.8. The method according to claim 4, wherein step b) includes moving thesurface generally axially between the open and closed positions.
 9. Themethod according to claim 5, wherein step b) includes partiallyobstructing the bypass flow path with the surface in the open position.10. The method according to claim 9, comprising opposing surfaces, andstep b) includes moving the opposing surfaces away from one another whenmoving from the closed position to the open position.